Electrokinesis and dielectrophoresis are two technologically important particle and fluid transport mechanisms in microscale flow channels. In the former, particle or fluid transport is produced by an applied electric field acting on a fluid or particle immersed in a fluid having a net mobile charge and is widely used as a mechanism for manipulating particles and conveying fluids in Microsystems.
Dielectrophoresis is particle motion produced by an electric field gradient on the induced dipole moment of a particle and the surrounding fluid. Rather than being linear in the applied field as is the case with electrokinesis, the dielectrophoretic potential field experienced by a particle is second order in the local electric field and is proportional to the difference between the particle and fluid polarizabilities.
Dielectrophoresis finds extensive application in manipulating, fusing, sorting, and lysing biological materials. However, prior art dielectrophoretic applications have the disadvantage that they require not only the use of networks of embedded electrodes that can be difficult and costly to fabricate to accomplish the desired result but also application of an alternating electric field having zero mean value. Because prior art dielectrophoretic separations apparatus depends upon the use of an applied electric field to effect separation, fluid flow through such an apparatus must be pressure-driven. Electrokinetic or electric field-driven flow cannot be used because of interferences with the electric field produced by the embedded electrodes and its attendant effect upon the separations process. Pressure-driven flow produces more hydrodynamic dispersion of an analyte than electrokinetically driven flow. Moreover, the prior art employs electrodes that produce field gradients in three dimensions, e.g., electrodes deposited on the top, bottom, or both surfaces of a channel. The dielectrophoretic effect decreases away from these electrodes. This decrease limits the maximum depth of the channels over which dielectrophoresis is effective. Channels cannot be made arbitrarily deep to support a desired volumetric flow rate or sample throughput. The depth dependence of the dielectrophoretic effect is also a source of analyte dispersion in a separation.
Articles entitled Dielectric Trapping Without Embedded Electrodes by E. B. Cummings and A. K. Sing in AIAA Ideal Electrokinesis and Dielectrophoresis in Arrays of Insulating Posts by Eric B. Cummings, AIAA February, 2001 describe scientific principle related to particle behavior in arrays of insulating structures. PCT US00/41929, Nov. 6, 2000 having a priority of application No. 60/163,523 describes trapping of particles using electrode-less dielectrophoresis for polarizable particles. All of these references are incorporated herein by reference.